Conventionally, for example in Japanese Unexamined Patent Application Publication No. 2010-260378A, a pneumatic tire is disclosed in which a plurality of protrusions (projections) extending in the tire radial direction is provided at predetermined intervals in the tire circumferential direction on the tire side portion (tire side surface) on the inner side in the vehicle width direction when the tire is mounted on a vehicle, and a plurality of recesses is provided over the tire circumferential direction and the tire radial direction on the tire side portion on the outer side in the vehicle width direction when the tire is mounted on a vehicle. When mounted on a vehicle, air flows uniformly toward the rear on the outer side in the vehicle width direction, but on the inner side in the vehicle width direction, the tire is disposed within the tire house, and other components such as the axle and the like are disposed nearby, so the flow of the air is easily disturbed. According to this pneumatic tire, an air flow circulation promotion effect and flow rectification effect are obtained and the air resistance is reduced by the protrusions provided on the tire side portion on the inner side in the vehicle width direction where the air flow is easily disturbed, and turbulent flow is produced when the vehicle is traveling by the recesses provided on the tire side portion on the outer side in the vehicle width direction, the drag force that tends to pull the tire backward due to the low pressure portion produced to the rear of the tire when traveling is reduced, so the fuel consumption is improved.
In the pneumatic tire disclosed in Japanese Unexamined Patent Application Publication No. 2010-260378A as described above, the height of the protrusions is not less than 0.5 mm and not more than 4 mm, but as a result of the research by the inventors and others, it has been found that the flow promotion effect and flow rectification effect that reduces the air resistance is significantly obtained when the protrusions exceed the above heights. However, if the height of the protrusions is not less than the above height, the protrusions are easily deformed by the centrifugal force associated with rotation of the tire and the force from the flow of the air, so the above effects are difficult to obtain sufficiently. Moreover, when the protrusions are deformed, the durability of the protrusions deteriorates. However, if deformation of the protrusions is suppressed too much, the cross-section of the protrusions will increase and the mass of the tire will increase, so the rolling resistance will tend to increase.